Синтезированы и исследованы новые керамические материалы на основе Rb3PO4 с высокой проводимостью по катионам рубидия в системе Rb3-2xPbxPO4. Введение катионов Pb2+ приводит к резкому возрастанию электропроводности ортофосфата рубидия за счет образования катионных вакансий, а при температурах 350-550oC и за счет стабилизации высокотемпературной кубической модификации Rb3PO4. В области высоких температур полученные электролиты обладают очень высокой ионной проводимостью, превышающей 10-1 S·cm-1 при 700oC, что выше значений, полученных ранее в аналогичных системах с добавками ионов цинка и кадмия. Обсуждаются факторы, влияющие на транспортные свойства исследованных материалов. DOI: 10.21883/FTT.2017.07.44599.402

New Rb 3 PO 4 -based ceramic materials with high rubidium-cation conductivity in the Rb 3–2 x Pb x PO 4 system have been synthesized and studied. Introduction of Pb 2+ cations leads to a sharp increase in the conductivity of rubidium orthophosphate due to formation of cation vacancies and, at temperatures 350–550°C, also due to the stabilization of high-temperature cubic modification Rb 3 PO 4 . At high temperatures, the electrolytes prepared have very high ion conductivity higher than 10 –1 S cm –1 at 700°C, which is higher than the values previously obtained in similar systems with additions of tin and cadmium ions. The factors influencing the transport properties of the materials under study are discussed.

New solid electrolytes with a high rubidium-cation conductivity, which are based on Rb3PO4 with partial substitution of three-charged yttrium, lanthanum, and neodymium cations for Rb+ cations, are synthesized and studied. Introduction of M3+ cations leads to an abrupt increase in the conductivity of rubidium orthophosphate due to the formation of cationic vacancies and stabilization of high-temperature cubic beta-modification of Rb3PO4. In all systems, the highest conductivity is observed in the single-phase region of beta-phase existence: it is similar to 10(-1) S cm(-1) at 700A degrees C and above 10(-2) S cm(-1) at 400A degrees C. The factors, which have an effect on the transport properties of studied electrolytes, are considered.

The earlier obtained data on the transport properties of cesium-conducting solid electrolytes based on cesium orthophosphate in the Cs3–2xMx II PO4 (MII = Mg, Ca, Sr, Ba), Cs3–3x PO4 (Mx III = Sc, Y, La, Sm, Nd) and Cs3–xP1–xZx VI O4 (Z = S, Cr, Mo, W) systems are analyzed. It is shown that, in addition to the conventional jump mechanism, the “paddle wheel” mechanism can play an important role in the ionic transport. This mechanism is associated with the orientation disordering of [PO4] tetrahedrons at the elevated temperatures, which leads to their rotation promoting “pushing” cesium ions into the accessible neighboring positions.

Solid electrolytes with rubidium-cation conductivity in the Rb 1− x Al 1 − x E x O 2 (E = Si, Ti, Ge) systems are synthesized. Their phase composition, temperature and concentration dependences of conductivity are studied. A high rubidium-cation conductivity (3 × 10 −3 S cm −1 at 300°C, 1.4 × 10 −2 S cm −1 at 700°C) is caused by the formation of rubidium vacancies as a result of Rb + + Al 3+ → E 4+ + V Rb substitution and stabilization of disordered structure of γ-KAlO 2 type.

New ceramic materials with a high rubidium-cation conductivity in Rb 3−2 x M x PO 4 ( M = Zn, Cd) systems have been synthesized and studied. It has been found that the introduction of Z n2+ and Cd 2+ cations leads to a sharp increase in the electrical conductivity of rubidium orthophosphate due to the formation of cation vacancies and the stabilization of the high-temperature cubic modification of Rb 3 PO 4 . The maximum conductivity has been observed in compositions with x = 0.15−0.30 and has the values of 10 −1 S cm −1 at 700°C and (2.0−2.5) × 10 −2 S cm −1 at 400°C. The factors influencing the transport properties of the materials under study have been discussed.

New materials of the K3 − 2x Pb x PO4 system with high potassium-cation conductivity have been synthesized and studied. It has been found that the introduction of Pb2+ cations substantially increases the conductivity of K3PO4 due to the formation of potassium vacancies and the stabilization of the high-temperature cubic structure of the orthophosphate. At low temperatures, the maximum conductivity has been observed in the composition range x = 0.15–0.20 and varies from ∼10−2 S cm−1 at 400°C to ∼10−1 S cm−1 at 700°C. The factors influencing the transport properties of the materials under study have been discussed.

Синтезированы и исследованы новые калийпроводящие твердые электролиты в системе K3 - 2xCdxPO4. В системе образуется широкая область твердых растворов со структурой высокотемпературной модификации ортофосфата калия, доходящая до x 0.35. Введение ионов кадмия приводит к резкому увеличению проводимости K3PO4 за счет образования калиевых вакансий. Максимальная проводимость составляет 10-2 См см-1 при 300°С и превышает 10-1 См см-1 при 700°С.

New potassium-conducting solid electrolytes of the K 3 − 2 x Cd x PO 4 system are synthesized and studied. A wide range of solid solutions reaching x ≈ 0.35 with the structure of high-temperature modification of potassium orthophosphate forms in the system. An addition of cadmium ions leads to an abrupt increase in the K 3 PO 4 conductivity due to the formation of potassium vacancies. The highest conductivity is approximately 10 −2 S cm −1 at 300°C and above 10 −1 S cm −1 at 700°C.

Data on transport properties of potassium conducting solid electrolytes based on K3PO4 in the systems K3−2xMxPO4 (M=Mg, Ca, Sr, Ba, Zn, Cd, Pb) and K3−xP1−xExO4 (E=S, Cr, Mo, W) have been analyzed. The results indicate that, in addition to the usual hopping mechanism, a substantial significance for ion transport in similar phases belongs to the “paddle wheel” mechanism. This mechanism is due to orientation disorder of the PO4 tetrahedra at elevated temperatures, which promotes moving K+ ions to the neighboring vacant positions.

The lithium-conducting solid electrolytes in the Li4 − 2x Cd x GeO4 (0 ≤ x ≤ 0.6) system are synthesized. Their crystal structure and temperature and concentration dependences of conductivity are studied. The specimens with the highest conductivity have a γ-Li3PO4-derivative structure. The solid solutions with x = 0.15–0.25 are stable at the room temperature, whereas the specimens with x ≥ 0.3 decompose yielding Li2CdGeO4 below 310 ± 10°C. Li3.6Cd0.2GeO4 solid solution exhibits the highest conductivity (5.25 × 10−2 S cm−1 at 300°C). The factors, which affect the conductivity of synthesized solid electrolytes, are considered.

Solid lithium electrolytes in the Li 4-3 x Fe x GeO 4 system were synthesized. Their phase composition, thermal behavior, and electrical conductivity were studied in the temperature interval 300–750°C. Introduction of Fe 3+ ions into lithium orthogermanate leads to the formation of a γ-Li 3 PO 4 -type structure and to a sharp increase in the conductivity, with a maximum reached at x = 0.075–0.15: about 10 −1 S cm −1 at 300°C and more than 1 S cm −1 at 700°C. The main current carriers are interstitial Li + cations weakly bound with the rigid framework. Owing to high conductivity, the electrolytes studied are of interest for use in high-temperature electrochemical devices.

New potassium-conducting solid electrolytes based on potassium monogallate in the K 2−2 x Ga 2− x V x O 4 system are synthesized and studied. It is found that an introduction of V 5+ ions leads to a considerable increase in the KGaO 2 conductivity due to the formation of vacancies in the potassium sublattice. The conductivity for optimal compositions is approximately 10 −3 S cm −1 at 400°C and above 10 −2 S cm −1 at 700°C. The results are compared with early obtained data for potassium monogallate dopped with four-charged cations.

Rubidium monoaluminate RbAlO2 has been studied by powder neutron diffraction and differential scanning calorimetry. A structural phase transition has been found at 1050°C. It is shown that the low-temperature modification RbAlO2 has the orthorhombic structure (Pnma, a = 0.5570(2) nm, b = 1.1189(4) nm, c = 1.5818(6) nm) close to the crystal structures of low-temperature modifications RbGaO2 and RbFeO2, not a face-centered cubic structure, as assumed previously.